I sought something else because Yaktrax wouldn't stay on properly. These are a 100% winner. Great traction on icy hiking trails. They are well made and are very easy to get on and off in a pinch.
I wear size 11 and found the large size a bit too large for my trail running shoes, but about right for boots. A medium fits better/no chain sagging on the trail shoes, but the large still performed well despite a little sagging. It would also probably just fit on the boots, but would be tight.
Also unlike Yaktrax they don't slip off and at least appear much more durable. Well they should be for twice the price of the Yaktrax Pros.

I was looking for a good alternative to yax track that provided better durability, security, and higher performance. Microspikes fit the bill. The elastic and stainless steel chains are bomber. I expect them to last many years. The elastic is sticky and the design is such that the things don't come off when in use. No matter how much you flail around, they don't pop off like some others can. They also offer very good traction on low grade terrain. They are also alot lighter than crampons. They can bail up a bit on heavy snow, but this product is exactly what I was looking for when I don't want crampons. They are very easy to get off, and a little more work to put on, but easier than crampons. I recommend them 100%. Sizing wise, I use a medium on men's 9.5-10 summer boots as well as 10.5 leather mountaineering boots. They fit quite well. And a small fits great on womens 8.